So the network is distributed across several "instances". While nothing stops fashy instances from existing, they are excluded from communication with other instances. Racists can be instance-wide blocked even if they're on another instance.

octodon.social: Nice domain. Run by a comrade. Not very moderated due to only one staff.

Ultimately, the choice is pretty unimportant. The only differences it makes are:

your domain.

the local timeline (if the instance is small, people may communicate within it and have fun there). This is partially the reason why there are so many specialized mastodon server.

trust (do you trust the owner to protect your privacy etc.?)

content policy and moderation (all the ones I've listed have good moderation, but you must still be aware that not all servers have that many moderators, so if you pick a low-staff instance, you will have to do some blocking by yourself)